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Acoustics
Published in Ali Jamnia, Practical Guide to the Packaging of Electronics, 2016
The phenomenon that fan noise is correlated to its rotational speed is associated with the blade geometry and aeroacoustics. Aeroacoustics is the study of the sound generated as aerodynamic forces interact with a solid surface. Developing fan blade geometry for noise reduction is a well-studied field, and new fan blade designs for noise reduction are proposed (Bianchi et al. 2012). In addition to the fan blade, aeroacoustics noise manifests itself when air is blown across sharp edges or corners. This happens often, when either printed circuit boards or fan guards are placed too close to the fan.
Feasibility verification of reducing the total sound pressure level of multiple cooling fans for fuel cell vehicle
Published in International Journal of Green Energy, 2023
Weijie Dong, Donghai Hu, Yuran Shen, Jianwei Li, Qingqing Yang
The cooling fan noise is a typical problem coupled with fluid dynamics and aeroacoustics (Angulo et al. 2022; Jang-Oh and Choi 2020). The finite volume method for solving the flow and sound fields has proven to be reliable (Barnoon, Toghraie, and Rostami 2020; Donghai et al. 2022). The Ffowcs Williams-Hawkings model for solving cooling fan aerodynamic noise problems has been widely used (Wang et al. 2022; Zanon et al. 2018). However, these methods cannot solve for the magnitude of cooling fan noise in the vehicle. Considering the application scenario of cooling fan, its noise affects both inside and outside the vehicle. Therefore, this paper combines existing aerodynamic acoustic methods with structural acoustic methods to solve the noise problem of multiple cooling fans. A mixed approach is used to address the noise problem of multiple cooling fans. First, the computational fluid dynamics and separation vortex method are applied to solve the flow field. The pressure and velocity data are imported into the computational aeroacoustics software to solve the frequency domain distribution. The main control equations used for noise solution in this study are as follows.
Unsteady stagnation-point flow of CNTs suspended nanofluid on a shrinking/expanding sheet with partial slip: multiple solutions and stability analysis
Published in Waves in Random and Complex Media, 2022
Sohita Rajput, Krishnendu Bhattacharyya, Ajeet Kumar Verma, Mani Shankar Mandal, Ali J. Chamkha, Dhananjay Yadav
Most of the problems are idealized as steady state (time-independent) due to the convenience in the analysis and the solution procedure, but it is not always consistent with the physical context. Hence, unsteadiness must be taken into consideration to make it more realistic. The simulation of time-dependent flow is crucial in technological areas, like helicopter aerodynamics, detonations, aeroacoustics, and turbomachinery. In 1958, Yang [28] reported the study of laminar boundary layer unsteady stagnation flow of incompressible fluid. In literature, the time-dependent flows due to expanding/shrinking sheets were discussed along with several physical aspects by many researchers [29–35]. Also, Bilal et al. [36] carried out 3-dimensional time-dependent study of water-based hybrid (CNT-ferric oxide) nanofluid on a wave-shaped fluctuating rotating disk. Regarding solution methodology, Ibrahim and Khan [37] solved the unsteady flow problem numerically by finite difference method and Hussanan et al. [38] reported analytic solutions of unsteady flow by the Laplace transformation method. While, Ahmad et al. [39] used semi-analytic method (HAM, Homotopy Analysis Method) to examine time-dependent viscoelastic flow. Recently, Anuar and Bachok [40] discussed unsteady stagnation-point micropolar flow of hybrid nanofluid and achieved solutions using ‘bvp4c’.
Towards overcoming the LES crisis
Published in International Journal of Computational Fluid Dynamics, 2019
For three decades a stated goal of research centers for turbulent flows has been to port the insights of DNS runs to simpler LES or RANS runs. This goal never materialised. A surprising development unforeseen at that time has been the replacement of sophisticated turbulence models for LES by monotonicity-induced LES (MILES) (Boris et al. 1992; Fureby and Grinstein 1999, 2002; Grinstein and Fureby 2002; Grinstein, Margolin, and Rider 2007; Grinstein 2016) or implicit LES (ILES) (Margolin and Rider 2002; Margolin, Rider, and Grinstein 2006). Following the argument that LES is not DNS and hence some scales will simply not be seen by the mesh used and therefore need to be damped, the idea is to use the intrinsic damping mechanisms of stable numerical schemes as the subgrid model. Obviously, the better the underlying scheme the further the cut-off frequency that can be resolved. While initially discarded as too simple to possibly be accurate, many studies (Boris et al. 1992; Fureby and Grinstein 1999, 2002; Grinstein and Fureby 2002; Margolin and Rider 2002; Margolin, Rider, and Grinstein 2006; Grinstein, Margolin, and Rider 2007; Grinstein 2016) have shown that MILES or ILES is in many cases more accurate than the most advanced LES models. One important finding was that the filter or limiter had to be non-linear, which automatically induces spatial and temporal variations, stochastic behaviour and backscattering. MILES has found widespread use in external aerodynamics and aeroacoustics in the aerospace and car industry, as well as the simulation of many environmental flows.